Automatic focus control for cathode-ray tubes



Nov. 4, 1947. P. F. GALELLA El AL 2,430,331

AUTOMATIC FOCUS CONTROL FOR CATHODE RAY TUBES Filed Sept. 14, 1944 Siam O uOmDOm am m 2 mh a J Patented Nov. 4, 1947 AUTOMATIC FOCUS CONTROL FOR CATHODE-RAY TUBES Pasquale F. Galella, New York, N. Y., and Joseph A. Brustman, Middletown, Conn., assignors to Remington Rand Inc., Buffalo, N. Y., a corporation of Delaware Application September 14, 1944, Serial No. 554,118

8 Claims.

This invention relates to cathode ray tubes, particularly the magnetic focus type used in television cameras and provides a means for automatically maintaining the focus in said tubes.

The invention provides means for automatically maintaining sharp focus of the electron beam in a cathode ray tube of the magnetic focus type wherein one or more electrode potentials affect focus.

The invention comprehends the provision of means for automatically maintaining a desired sharpness of focus in the electron beam of a cathode ray tube during variations in current in the focusing coil and also during variations in supply voltage at the control electrodes. The invention is incorporated in means that operates to maintain a desired degree of sharpness of the beam focus in cathode ray tubes during variations in focusing current, variations in supply voltage, and variations in temperature of the focusing coil windings by automatically maintaining a constant predetermined relation between focusing current and focusing anode voltage.

The invention provides a translating device having an input circuit coupled with a circuit through a focusing coil of a cathode ray tube responsive to variations in current in said focusing coil for translating said variations into variations in voltage in an output circuit of said translating device connected with a focus control anode in said tube for varying the voltage of said focus control anode synchronously with current variations in said focusing coil to maintain a desired sharpness of focus of an electron beam in the cathode ray tube.

The invention comprehends the provision of means for varying synchronously the voltage of a focus control anode in predetermined relation with variations in current in a focusing coil for automatically maintaining a desired sharpness of focus of the electron beam in a cathode ray tube and means for varying the operation of the firstmentioned means to obtain a desired sharpness of focus.

The invention provides means for automatically and normally maintaining a desired rela tion between focus control anode voltage and focusing coil current during Variations in focusing coil current, variations in temperature of the focusing coil winding, other variations in the circuit affecting conductivity through said focusing coil, and variations in supply voltage, together with means for adjusting the relation between focusing coil current and focusing anode voltage for obtaining a desired sharpness of focus in main types of cathode ray tubes.

The single figure on the drawings shows a wiring diagram of one group of circuits used with various apparatus and illustrates one way of practicing the present invention.

The invention is particularly adaptable for use with television camera pick-up tubes and the drawing discloses a means for automatically maintaining a sharp focus of the electron beam in such a tube. It is to be understood that the invention may be applied to all types of cathode ray tubes in which the focusing of an electron beam is produced by means of combined magnetic and electrostatic fields.

A television pick-up tube is indicated diagrammatically at I and may be of low velocity scanning beam type having a mosaic 2 at one end of the tube and an electron gun at the opposite end. This gun has a heater element 3 and an electron emitting cathode 4. Associated therewith is a control grid 5, a second grid 6 and a focus control anode I. The anode l is usually connected to a conductive coating on the inner surface of the glass envelope containing the various electrodes above described. The tube may also include other electrodes not shown in the drawing all of which are constructed and insta led in the glass envelope forming the assembly referred to as tube I, that are made according to to practice now well-known in the art and a further description and illustration thereof is not believed necessary to the disclosure of the present invention.

A magnetic focusing coil 8 of conventional form is engaged about tube l in a manner well-known in the art and is used in focusing on mosaic 2 the electron beam emitted by the electron gun. One end of focusing coil 8 is connected by wire 9 with one terminal of a current regulator ii! having the other terminal connected by wire H to the positive terminal of a source of electrical energy indicated at l2. The negative terminal of the source of energ I2 is connected to a common ground by wire l3. The other end of the focusing coil is connected by wire I to one terminal of resistor l5 havin the opposite terminal connected to the common ground by wire I6. This completes the circuit for energizing the focusing coil 8 to provide the magnetic field for focusing the electron beam.

The current regulator lll operates to normally maintain the approximate value of focusing current in coil 8 to provide for normally maintaining the focus of the electron beam in tube Current regulator Ill may be of an suitable type wellknown in the art, such as the usual resistance type current regulator enclosed in an envelope in a gaseous atmosphere. A well-known form of such device is known as an Amperite current regulator.

Wire l4 also provides a circuit connection with the cathode ll of a translating device l3 which may be in the form of the usual triode electron tube. Tube l8 forms a regulator tube having input and output circuits that are operated in response to variations in current in the circuit through focusing coil 8. The variations may be caused by variations in voltage of the energy supply source I 2, variations in the regulating characteristic of regulator It, and variations in the resistance of focusing coil 8 resulting from temperature changes. Any of these variations will vary the current flow in the focusing coil circuit to which the input circuit of tube I8 is responsive.

The input circuit of tube I8 is completed from cathode I! through wire M to resistance I5 and then through wire IE to ground. Grid I9 is included in the input circuit and has a wire connection 20 to the adjustable contact of variable resistor 2| included in a resistance network with resistors 22 and 23. Resistors 2|, 22 and 23 are connected in series in the network as illustrated in the drawing. The connection between the terminals of resistors 2| and 23 has a wire connection 24 through resistor 25 with the negative terminal of a source of electrical energy indicated at 25, while the positive terminal of source 26 is connected to the common ground by wire 21. This completes the grid cathode circuit of tube l8 forming the input circuit in which the adjustment of the movable contact of resistor 2| may be varied to change the value of negative potential applied to grid 9 for adjusting the sharpness of focus in tube in a manner that will be hereinafter described.

The opposite terminal of resistor 23 from that connected to resistor 2| is connected to the common ground by wire 28. The terminal of resistor 22 opposite to that connected to resistor 2| has a wire connection 29 connected to one electrode of gaseous voltage regulator tube 30. A second gaseous regulator tube 3| is connected in series with tube 30 and through a wire 32 to the common ground.

Control tube 8 has an anode 33 connected by wire 34 with focus control anode and one terminal of resistor 35. The other terminal of resistor 35 is connected through wire 29 with gaseous regulator tube 30 and through resistor 36 to the positive terminal of a source of electrical energy indicated at 26 having the negative terminal connected by wire 21 to the common ground. The connection from resistor 36 to the positive terminal of electrical source 26 is also connected to the common ground through condenser 37. The source of electrical energy 26 supplies a positive potential for anode 33 of control tube l8 and focus control anode 1. The gaseous voltage regulators 30 and 3| operate to maintain substantially uniform voltage across the resistance network in- 4| cluding resistors 2 l, 22 and 23 and the circuit connected therewith.

The source of electrical energy 26 supplies the energy for the operation of both the input and output circuits of control tube I8 so that any variations in voltage in supply 26 are applied proportionately to maintain a balanced condition and operation in the input and output circuits of tube l8.

A by-pass condenser at! is connected between focus control anode l and cathode 4 and acts as a filter in view of the cathode and one terminal of condenser 40 being connected to the common ground.

The control tube or translating device lit with its input and output circuits coupled to the circuit with focusing coil 8 and focus control anode 1, provides control means for maintaining the desired condition of focus of the electron beam in tube This is due to the fact that the current flowing in focusing coil 8 has a direct relation to the voltage applied to anode i. This relationship is such that the focusing coil current-anode voltage characteristic is linear over a considerable range so that equal variations in focusin current when accompanied by corresponding variations in anode voltage will maintain a uniform condition of focus of the electron beam. It will maintain a sharp focus if the electron beam is originally adjusted to provide a sharp focus.

In order to obtain a sharp focus resistor 2| is adjusted to vary the negative bias voltage of grid l9 and thereby the Voltage applied to anode of tube I. This adjustment provides a means for selecting the proper value of voltage for anode in relation to focusing coil current for sharp focus of the electron beam in tube Whenever this sharp focus condition is obtained, control tube I8 with its input and output circuits will automatically operate to maintain a sharp focus.

Whenever variations occur in the current flowing in focusing coil 8 caused by variations in sup ply voltage, variations in the characteristics in regulator ID, or variations in the temperature of the focusing coil winding, or a combination of all three conditions, the variation in current will be transmitted to the input circuit of tube H3. The variation in current in the focusing coil 8 causes a variation in voltage drop across resistor l5 also included in thecathode-grid circuit of control tube is. This variation in voltage across resistor l5 causes a variation in the input circuit of tube I8 which is transmitted to the output circuit thereof. For example, when the current flowing through focusing coil 3 and resistor I5 decreases from that normally required for the desired condition of focus, the voltage drop across resistor l5 decreases correspondingly and causes cathode I! to become more negative with respect to grid l9 thus decreasing the internal plate-cathode resistance of control tube I8 and the voltage drop across said tube making the voltage applied to anode 1 less positive.

Whenever the current in focusing coil 8 increases above that required for the normal or desired condition of focus, there will be an increase in current through resistor l5 resulting in an increase in voltage drop across resistor I5 thereby producing a change in the input circuit of tube l8 so that cathode H will become more positive with respect to grid l9 causing the internal resistance of tube H to increase thus increasing the voltage drop across tube l'8 and making the voltage applied to anode more positive.

It will therefore be apparent that any variation in current in focusing coil 8 will result through the operation of control tube I8 and its input and output circuits to obtain a corresponding variation in voltage applied to anode 1 for automatically maintaining the desired condition of focus Of the electron beam in tube I.

In addition to variations in focusing current in coil 8, variations in anode voltage supply may occur despite the regulating action of gaseous regulators 30 and 3|. Likewise the normal grid bias for regulator tube 18 obtained through wire 20 from the adjustable connection with resistor 2! may vary since this bias voltage is also obtained from the resistance network consisting of resistors 2i, 22, and 23 connected to wire '29 across the anode voltage supply for the output circuit of tube l8. By connecting the source of negative potential from supply 25 to the connection between resistors 2| and 23 through resistor 25, the input circuit for tube It? is controlled simultaneously with the output circuit thereof so that variations in anode voltage supply will provide similar variations in the input circuit to maintain the proper value of grid bias on control tube l8 for a balanced operation of tube l8 to maintain the desired condition of focus of the electron beam in tube By varying the current value through focusing coil 8 in any desired manner, such as by means of a variable resistance in wire 9, the focusing field strength may be adjusted without affecting the sharpness of focus. This variation of focusing field strength changes the deflection sensitivity for varying the picture size while the control of focus is automatically maintained by the input and output circuits of tube l8.

The sources of electrical energy shown at 12 and 26 may be of any conventional form. A single source of electrical energy may be used. Source 12 may be a suitable battery while source 25 may be a, dynarnotor operated from the source [2.

The invention claimed is:

1. An automatic focus control for cathode ray tubes wherein the tube has a magnetic focusing coil and control electrodes for controlling electron beam focus having in combination, a focusing coil circuit having said focusing coil in series with a current supply source, and focus control means having an input circuit responsive to variations in current in said focusing coil circuit and an output circuit controlled by said input circuit coupled with the circuit to one of said control electrodes to vary the anode voltage of said electrode in unison with current variations in said focusing coil circuit,

2. An automatic focus control for cathode ray tubes having a focusing coil and a focu control anode, comprising a focusing coil circuit having said focusing coil and a current regulator in series with a current supply source, and focus control means having an input circuit coupled with said focusing coil circuit responsive to variations in current in said focusing coil circuit, and an output circuit responsive to variations in said input circuit coupled with said focus control anode for varying the voltage of said anode synchronously with current variations in said focus ing coil for cooperation in maintaining a sharp focus.

3. An automatic focus control for cathode ray tubes having a focusing coil and a focus control anode, comprising circuit means for energizing said focusing coil, and focus control means having an input circuit coupled with said circuit means and responsive to current variations in said focusing coil, an output circuit responsive to variations in said input circuit coupled with said focus control anode for varying the potential on said anode in synchronism with current variations in said focusing coil, and means in one of said input and output circuits for controlling and adjusting the relation between said anode potential and focusing coil current.

4. An automatic focus control for cathode ray tubes having a focusing coil and a focus control anode, comprising a circuit for energizing said focusing coil, and focus control means having a translating device, an input circuit for said translating device coupled with said first-mentioned circuit and responsive to current Variations in said focusing coil, and an output circuit conn'ectcd with said translating device responsive under the control of said device to variations in said input circuit, said output circuit being coupled with said focus control anode for vary ing the potential of said anode in synchronism with current variations in said focusing coil for maintaining a uniform condition of focus.

5. An automatic focus control for cathode ray tubes having a focusing coil and a focus control anode, comprising a circuit for energizing saidfocusing coil, and focus control means having a translating device, an input circuit for said translating device coupled with said first-mentioned circuit and responsive to current variations in said focusing coil, and an output circuit connected with said translating device responsive under the control of said device to variations in said input circuit, said output circuit being coupled with said focus control anode for varying the potential of said anode in synchronism with current variations in said focusing coil for maintaining a uniform condition of focus, and means for controlling the operation of said translating device for varying the relation between focusing coil current and focus control anode potential for controlling the sharpness of focus.

6. An automatic focus control for cathode ray tubes having a focussing coil and a focus control anode, comprising circuit means for energizing said focusing coil. and focus control means including a translating device having an input circuit coupled with said circuit means and responsive to current variations in said focusing coil, an output circuit for said translating device responsive to variations in said input circuit connected with said focus control anode for varying the potential of said anode in synchronism with current variations in said focusing coil, and means connected in circuit with said translating device for adjusting the focusing coil currentfocus control anode potential relation to control the sharpness of focus in said tubes.

7. An automatic focus control for cathode ray tubes having a focusing coil and a focus control anode, comprising circuit means for energizing said focusing coil, a translating device, an input circuit for said translating device coupled with said circuit means and responsive to current variations in said focusing coil and circuit means, an output circuit connected to said translating device responsive through said translating device to variations in said input circuit and coupled with said focus control anode for varying the potential of said anode in synchronism with current variations in said focusing coil, and voltage regulating means coupled with said input and output circuits of said translating device for uniformly regulating the voltage in said circuits be maintained in said tubes.

8. An automatic focus control for cathode ray tubes having a focusing coil and a focus control anode, comprising circuit means for energizing said focusing coil, a translating device, an input circuit for said translating device coupled with said circuit means and responsive to current variations in said focusing coil and circuit means, an output circuit connected to said translating device responsive through said translating device to variations in said input circuit and coupled with said focus control anode for varying the potential of said anode in synchronism with current variations in said focusing coil, and voltage regulating means coupled with said input and output circuits of said translating device for uniformly regulating the voltage in said circuits, and means for varying the potential in said input circuit operable to change the focusing coil our- 8 rent-focus control anode potential relationship whereby a substantially uniform sharpness of focus may be maintained in the operation of said tubes.

PASQUALE F. GALELLA. JOSEPH A. BRUSTMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,255,485 Dome Sept. 9, 1941 2,078,644 Swedlund Apr. 27, 1937 2,116,671 Dowsett et a1 May 10, 1938 2,051,372 Farnsworth Aug. 18, 1936 2,369,631 Zanarini Feb. 13, 1945 2,137,262 Bowman-Manifold Nov. 22, 1938 1,923,252 Brolly Aug. 22, 1933 

